1. Field of the Invention
This invention relates to an outboard motor, and more particularly to an improved exhaust arrangement for outboard motors having four-cycle internal combustion engines.
2. Description of the Related Art
Outboard motors are generally attached to a transom of a watercraft and are used to propel the watercraft. These motors comprise an internal combustion engine arranged to drive a water propulsion device, such as a propeller.
The outboard motor is connected to the watercraft in a manner that permits the motor to turn from side-to-side about a vertically extending axis in order to steer the watercraft. In addition, the motor is tiltable about a generally horizontal axis in order to trim the motor.
For a variety of reasons, outboard motors are constructed to be very compact. Such motors also must to be substantially self-contained. Thus, the cooling, exhaust and silencing systems are substantially contained within the motor.
In an outboard motor employing a four-cycle engine, a source of lubricant is required to hold lubricant that is circulated through the engine. In order to provide adequate storage capacity within the compact arrangement of the outboard motor, the lubricant tank is generally positioned in the driveshaft housing below the engine. An exhaust pipe depends from the engine into the driveshaft housing and is positioned adjacent to or through the lubricant tank. Thus, in some outboard motors, the lubricant tank generally encircles the exhaust pipe. Such positioning of the lubricant tank exposes the tank to hot exhaust gases which can heat the lubricant in the lubricant tank. Excessive heat degrades the lubricant, possibly leading to engine damage.
Outboard motors also conventionally employ an open-loop cooling system that draws cooling water from the body of water in which the outboard motor is operated (e.g., a lake or an ocean). The cooling water is directed through cooling passages in the engine in order to cool the engine, and is also directed onto the outer walls of the lubricant tank and around the exhaust pipe in order to cool the lubricant and exhaust.
A lower portion of the exhaust pipe is often connected to a coolant outlet, which directs coolant into the pipe. Injecting coolant into the exhaust system both cools the exhaust and enhances engine silencing. The mixed coolant and exhaust gas are discharged into the body of water through an exhaust system discharge.
It has been found that when coolant such as saltwater is vigorously mixed with exhaust gases, certain corrosive gases can be generated. Because the coolant and exhaust gases are usually mixed in the lower portion of the exhaust pipe, the corrosive gases tend to concentrate their effect on the lower portion of the exhaust pipe, and thus the lower end or lower opening of the exhaust pipe may be corroded even when the rest of the exhaust pipe remains relatively unaffected by corrosion.
In a conventional outboard motor, an upper end of the exhaust pipe is typically fitted and secured to an exhaust guide portion of the motor. Additionally, caulking and/or gaskets may be used to create a sealing fit of the upper end of the exhaust pipe and the exhaust guide. Since the lubricant tank often surrounds the upper end of the exhaust pipe, it can be very difficult to disassemble or remove the exhaust pipe when service is required, such as when corrosion is noted on the lower end of the exhaust pipe. This arrangement leads to waste of time and materials because not only is it difficult and time-consuming to replace the entire exhaust pipe, but it is also wasteful to replace the entire exhaust pipe when only the lower portion of the pipe is corroded.
Accordingly, there is a need in the art for an outboard motor having an exhaust system allowing for relatively easy and inexpensive change-out of portions of the exhaust system that are most likely to become corroded and require replacement. Such an exhaust system would save effort by making it easier to replace corroded parts; it would also save in materials costs by requiring replacement of only a relatively small portion of the exhaust system rather than the entire exhaust pipe when only a portion of the exhaust pipe exhibits corrosion.
In accordance with an aspect of the present invention, an outboard motor is provided having a power head including an internal combustion engine, a driveshaft housing depending from the power head, and a lower unit depending from the driveshaft housing. An upstream exhaust pipe receives exhaust gases from the engine and depends into the driveshaft housing. A downstream exhaust pipe is formed separately from the upstream exhaust pipe and communicates therewith. The downstream exhaust pipe opens into an exhaust chamber formed in the lower unit and is removable from the driveshaft housing independently from the upstream exhaust pipe.
In accordance with another aspect, the invention provides an outboard motor comprising a power head, a driveshaft housing depending from the power head, a lower unit depending from the driveshaft housing, an internal combustion engine enclosed within the power head and adapted to drive a crankshaft, and an exhaust system adapted to communicate exhaust products from the engine to an exhaust discharge located on the lower unit. The exhaust system has an upstream exhaust pipe, a downstream exhaust pipe, and an exhaust ipie support member. The upstream exhaust pipe depends into the driveshaft housing and is supported by the exhaust pipe support member. The downstream exhaust pipe depends from the exhaust pipe support member and through an opening formed through a bottom wall of the driveshaft housing. Also, the downstream exhaust pipe has a mount portion adapted to releasably engage the driveshaft housing. The downstream pipe and the opening are configured so that the downstream exhaust pipe can be drawn downwardly through the opening to remove the downstream pipe from the driveshaft housing.
In accordance with yet another aspect of the invention, an outboard motor has a power head including an internal combustion engine, a driveshaft housing depending from the power head, and a lower unit depending from the driveshaft housing. An exhaust pipe assembly guides exhaust products through at least a portion of the driveshaft housing, and includes an upstream exhaust pipe section and a downstream exhaust pipe section. The downstream exhaust pipe section extends through an opening in a bottom wall of the driveshaft housing. The exhaust system further includes means for removably securing the downstream pipe section to the driveshaft housing in a manner so that an upper end of the downstream pipe section communicates with a lower end of the upstream pipe section and the downstream pipe section is removable by drawing the downstream pipe section downwardly through the opening.
In accordance with a still further aspect, the present invention provides an outboard motor comprising a power head, a driveshaft housing depending from the power head, a lower unit depending from the driveshaft housing, and an internal combustion engine enclosed within the power head and adapted to drive a crankshaft. The crankshaft rotatably communicates with a propulsion device provided on the lower unit. A coolant chamber is defined within the driveshaft housing. An exhaust system is provided and is adapted to communicate exhaust products from the engine to an exhaust discharge disposed at the lower unit. The exhaust system has an upstream exhaust pipe, a downstream exhaust pipe, and an exhaust pipe support member. The upstream exhaust pipe depends into the driveshaft housing and is supported by the exhaust pipe support member. The downstream exhaust pipe depends from the exhaust pipe support member and is configured to be removable from the driveshaft housing independent of the upstream exhaust pipe. A drain passage is formed through a wall of the downstream pipe and communicates with the coolant chamber.
Further aspects, features and advantages of the present invention will become apparent from the Detailed Description of Preferred Embodiments which follows.